Magnetic core



May 6, 1952 e. G. SOMERVILLE 2,595,820

MAGNETIC CORE Filed Aug. 20, 1949 Fig 2. 4

Inventor: Gareth G. Somevville,

His At 'borne ld.

Patented May 6, 1952 MAGNETIC CORE Gareth G. Semen-ville, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application August 20, 1949, sci-n1 No. 111,443

2 Claims. 1

This invention relates to magnetic cores and more particularly to-improvements in so-called curved cores for stationary electromagnetic induction apparatus.

A curved core comprises at least one substantially closed magnetic circuit consisting of fiat- Wise curved usually radially nested .laminations. In many such cores it is desirable to have at least one joint so that the magnetic circuit may be opened for the purpose of mounting a preformed conductive winding on what is generally referred to as the winding leg of the core, after which the joint is reclosed. In one form of such joint the adjacent ends of each lamination layer overlap each other and the areas of overlap of the ends of each layer or lamination are transversely, and usually radially, aligned. However, such a joint will be twice as thick as the rest of the core and this is often objectionable and wasteful of space and material.

In a modified joint of this general type the ends of alternate lamination pieces are in butt contact and the butt joints in these alternate layers are aligned transversely with the overlap joints in the other set of alternate layers. Such a joint has good magnetic and physical characteristics because in a plane through all of the aligned butt joints there will be as much magnetic material as in the rest of the core because in that plane the set of alternate laminations whose ends are overlapped provides half the total number of laminations each beingof double thickness due to the overlap so that there will be 100 per cent magnetic material in that plane. Also, the thickness of the joint or core :in that plane is only one and one-half times the thickness of the rest of the core. However. when the core is made by individually pre-cutting to length the individual lamination pieces and then assembling those pieces in radiallypnested layers it is necessary to have two difierent packs or groups of laminations from which the core is assembled because the lamination Pieces do not progressively increase or decrease in length depending upon whether one progresses from the inside layer to the outside layer or vice versa. This is because the length of the overlap in, say for example, the innermost layer will ordinarily be longer than the amount by which the circumference of the next innermost layer will exceed the circumference of the innermost layer because the progressive increase in circumference of the layers when progressing from the inner layer to the outer layer .is determined principally by the thickness of the layers and 2 this is ordinarily of the order of only ten to fourteen mils, whereas the overlap extends typically for three-eighths of an inch. Consequently,

each of the layers in the set of alternate layers whose ends make butt contact With each other are shorter than the next adjacent layers in side them whose ends overlap each other. As a result, all of the lamination pieces cannot readily be cut in a continuous process on an ordinary index shearing machine which turns out pieces Whose lengths all increase (or decrease) progressively. Therefore, it is necessary to provide two different packs or groups of lamination pieces which are cut separately and from which an assembler takes the pieces alternately in assembling the core and this of course in creases the amount of labor required and the difficulty of assembling the core.

In accordance with this invention there is provided a novel joint in which the adjacent ends of each lamination layer or lamination piece overlap each other but the aligned areas of overlap in one set of alternate or non-adjacent layers are displaced circumferentially irom the aligned areas of overlap in the other set of non-adjacent or alternate lamination layers in such a mannerthat there is butt contact between the end (or beginning) of one set of alternate lamination pieces and the beginning (or end) of the lamination pieces in the other set of alternate or non-adjacent layers. In this manner the joint will never have less than per cent cross section of magnetic material in any plane and it will never have a thickness greater than per cent of the rest of the core where there is no joint, while at the same time every lamination layer is longer than the layers inside it and is shorter than the layers outside it.

An object of the invention is to provide a new and improved magnetic core.

Another object of the invention is to provide a new and improved joint for magnetic cores.

A further object of the invention is to provide a new and improved curved magnetic core for stationary electric induction apparatus.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing Fig. 1 is a perspective View of a stationary electric induction apparatus embodying the invention, Fig. 2 is an enlarged detailed side view of one of the joints of one of the two core parts shown in Fig. 1, Fig. 3 is a view of a partially assembled or stacked core in preliminary circular form, and Fig. 4 is a pack or stack of lamination pieces from which the core is assembled in the manner shown in Fig. 3.

Referring now to the drawing and more particularly to Fig. 1 there is shown therein a magnetic core of the so-called divided or distributed type having two similar portions 2 and 2. These portions are shown, by way of example, as being rectangular in configuration and they each have a generally straight winding leg 3 and 3' respectively. These winding legs are placed back to back so to speak with the remaining or yoke parts extending away from each other. A conductive winding or windings 4 is indicated schematically as being mounted on the common central winding leg 3-3.

The core portions 2 and 2' are of the curved type consisting of flatwise bent radially nested laminations. Each core part is provided with at least one separable joint 5 and 5' respectively. These joints are preferably adjacent the ends of the respective winding legs so that when they are open the conductive winding 4 may readily be slid into place and then the joints can be closed. The opening of the joints is made possible by a flexing or hinge action of the generally opposite parts 6 and 6 of the cores.

The joints 5-5' are of novel construction as is shown more clearly in Fig. 2. In this figure l the adjacent ends of one set of non-adjacent or alternate laminations I, I, 1 etc., overlap each other with an area of overlap indicated at 8 and these areas of overlap are all transversely aligned in the core. As shown they are radially aligned but this is not essential and they could obviously be aligned in other ways. Likewise the adjacent ends of the remaining or other set of alternate or non-adjacent lamination layers 9, 9 and 9" all overlap each other with an area of overlap l0 and these areas of overlap ID are similarly transversely aligned through the core. However, the aligned areas of overlap ID are circumferentially displaced from the aligned areas of overlap 8 by the distance I I. Usually the lengthwise extent of the overlaps 8 and It will be equal and therefore the circumferential displacement of the two different sets of aligned overlaps will also be equal to the extent of each overlap but that obviously is not essential. At all events, the circumferential displacement is such that one end of each of the layers 1, I and "I" makes butt contact respectively with the opposite end of the layers 8, 9' and 9". Thus, for example, starting at the outside of the core and progressing from the start or beginning of the layer 9 it will be seen that the end of the layer 9 makes butt contact with the beginning of the layer 1'. Likewise, the end of the layer 9 makes butt contact with the start of the layer I and in like manner the end of the layer 9 makes butt contact with the beginning of the layer I.

A characteristic of this joint construction is that the minimum magnetic cross section of the joint is 100 per cent the magnetic cross section of the rest of the core. This will really be apparent from the following. Considering transverse planes I2 and I3 through the core proper on both sides of the joint 5, it will be seen that they contain as much magnetic material as is in the cross section of each lamination layer multiplied by the number of layers, that is to say 100 per cent magnetic material. The worst plane through the joint from the point of view of the amount of magnetic material in it is the plane I4 through the aligned butt joints and it will be seen that in this plane there is also per cent magnetic material. That is to say, there are six continuous portions of magnetic strip passing through this plane and as there are only six lamination layers shown it follows that there is 100 per cent magnetic material in the plane I4. It will also be observed that the thickness of the joint in the plane I4 is that of nine lamination layers so that the joint has a thickness of per cent the thickness of the core proper in the plane I2 where the laminations are all in contact with each other and there is no empty space between them.

In constructing the core a reel of magnetic strip material, typically cold rolled high reduction silicon steel known to the trade as SX-lO, of 10,.12 or 14 mils thickness, is cut into pieces of progressively varying length and the pieces are stacked in the order of their length in the manner shown in Fig. 4. Simultaneously with the cutting of each piece, three holes are punched in it. Two of the holes, I5 and I6, are punched a distance from the respective ends of the pieces equal to half the extent of the overlaps 8 and I0 and the third hole I1 is spaced from the hole I5 by the extent of the overlaps 8 and II].

In assembling the core and forming the joint the longest piece may be fiatwise bent into a circle so that the hole I5 is brought into alignment with and beneath the hole I6 and a pin or rod I8 is passed through the aligned holes so as to'hold the strips together. The next longest piece may then be taken from the top of the pack, reversed lengthwise, and its hole I6 placed underneath the hole I! of the first or longest piece and a second pin or rod I9 is then inserted through these aligned holes. The new piece is then brought around clockwise into a circle until its other end hole I5 can be fitted over the inner end of the rod I9 and its hole IT can be fitted over the inner end of the rod I8. In this manner the core is built up one piece at a time from the outside to the inside. After the core has been stacked or assembled to the proper thickness, it is shaped by means of mandrels to any desired configuration after which it is strainrelief annealed.

While there has been shown and described a particular embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A curved magnetic core for stationary electromagnetic induction apparatus comprising, a plurality of radially nested flatwise curved lamination pieces of magnetic strip material, each of said pieces constituting a separate layer of said core and each being longer than the circumference of said core at its location whereby the ends of each piece are in overlapping relation, the areas of overlap of the ends of one set of alternate pieces being aligned transversely, the areas of overlap of the ends of the remaining set of alternate pieces being aligned transversely and off-set circumferentially relative to the transversely aligned areas of overlap of the ends of the first alternate set of pieces, one corresponding end only of each piece in said first set of alternate pieces being in substantial butt contact with an-opposite end only of an adjacent piece of the remaining set whereby all of said areas of overlap constitute a core joint which in no transverse plane through it has less than 100 per cent magnetic material and more than onehalf times the radial thickness of the sum of thicknesses of all of the said pieces.

2. A curved magnetic core for stationary electromagnetic induction apparatus comprising a plurality of radially nested flatwise curved lamination pieces of magnetic material, each of said pieces constituting a separate layer of said core and each being longer than the adjacent piece inside it and shorter than the adjacent piece outside it, each of said pieces being longer than the circumference of said core at its location whereby the ends of each piece are in overlapping relation, the areas of overlap of One set of alternate pieces being equal and being aligned radially, the areas of overlap of the ends of the.

remaining set of alternate pieces being equal to the areas of overlap of the ends of the first set of pieces and being aligned radially and oif-set circumferentially relative to the radially aligned areas of overlap of said first set of alternate pieces, one corresponding end only of each piece in said first set of alternate pieces being in substantial butt contact with an opposite end only of an adjacent piece of the remaining set whereby all of said areas of overlap constitute a core joint which in no transverse plane through it has less than 100 per cent magnetic material and more than one and one-half times the radial thickness of the sum of the thicknesses of all of said pieces.

GARETH G. SOMERVILLE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,456,458 Somerville (B) Dec. 14, 1948 2,477,350 Somerville (A) July 26, 1949 2,478,029 Vienneau Aug. 2, 1949 2,489,625 Dornbush Nov. 29, 1949 FOREIGN PATENTS Number Country Date 622,538 Great Britain May 3, 1949 

